This invention relates to mullite and more particularly to the preparation of mullite whiskers.
Various methods have been use to produce mullite whiskers.
U.S. Pat. No. 3,104,943, entitled "Spinnable Mullite Fibers and Their Preparation," which issued to Kenneth L. Berry on Sept. 24, 1963, discloses a method whereby mullite fibers are crystallized from a vapor phase derived from heating sources of Si, Al, O.sub.2, and S in an atmosphere containing at least 1 percent H.sub.2 at 800.degree.-1200.degree. C.
U.S. Pat. No. 3,607,025, entitled "Silica-Deficient Mullite Fiber and a Process for Its Production," which issued to Howard W. Jacobson on Sept. 21, 1971, discloses a process whereby an alkali halide and AlCl.sub.3 are contacted with a silica source in the presence of an oxidizing gas at 1000.degree.-1350.degree. C. The fibers produced, however, are not stoichiometric mullite (72.8% Al.sub.2 O.sub.3 and 28.2% SiO.sub.2) b composition but do exhibit the x-ray pattern of compositional mullite. The fibers are silica deficient containing 82-99 percent by weight Al.sub.2 O.sub.3 and the remainder SiO.sub.2. Also in the process, the fibers must be leached out from a solidified melt with water or dilute acid solution.
U.S. Pat. No. 3,073,770, entitled "Mullite Synthesis," which issued to William R. Sinclair and John C. Williams on Jan. 15, 1963, discloses a process whereby a reaction sputtered film of Al.sub.2 O.sub.3 and SiO.sub.2 is heated to at least 1000.degree. C. to form mullite whiskers.
Bella Locsei in "Mullite Formation in the Aluminum Fluoride-Silica System" (AlF.sub.3 -SiO.sub.2), Nature, No. 4779, June 3, 1961, discloses that mullite can be formed from reagent grade aluminum fluoride (AlF.sub.3) with or without structural water and silica gel or silica glass by heat treatment in an oxidizing atmosphere.